Conventionally, there is known a motor driving device that includes a microcomputer having a CPU, a driving IC for generating drive pulses in response to a signal transmitted from the CPU, and an inverter for supplying a driving current to a motor in response to the drive pulses transmitted from the driving IC.
A motor control system employed in the conventional motor driving device is disclosed in, e.g., Japanese Patent Application Publication No. 2010-22150. In the motor control system of Japanese Patent Application Publication No. 2010-22150, a PWM signal output unit corresponding to the driving IC is mounted together with a microcomputer having a CPU on the same chip (see paragraphs 0009 and 0014).
If the driving IC is mounted together with the microcomputer on the same chip as in the motor control system disclosed in Japanese Patent Application Publication No. 2010-22150, the chip including the microcomputer and the driving IC needs to be replaced as a whole in order to implement different variations depending on the kind and purpose of a motor. Meanwhile, if the driving IC and the microcomputer are installed independently of each other, the variations of a motor driving device can be broadened by combining different kinds of driving ICs and different kinds of microcomputers. Therefore, in order to implement different variations, it is preferable to install the driving IC and the microcomputer independently of each other.
However, when the driving IC and the microcomputer are installed independently of each other, it is sometimes the case that the output voltage range of the microcomputer and the input voltage range of the driving IC differ from each other. In that case, if the voltage signal outputted from the microcomputer is directly inputted to the driving IC, the input voltage range of the driving IC cannot be used in its entirety. Thus, the operation of the motor is limited. In particular, if the upper limit and the lower limit of the output voltage range of the microcomputer are respectively different from the upper limit and the lower limit of the input voltage, a reduction in the resolution of a voltage signal cannot be avoided by merely adjusting the magnification of the output voltage of the microcomputer.
At least an embodiment of the present invention provides a motor driving device capable of suppressing a reduction in the resolution of a voltage signal supplied from a microcomputer to a driving IC.